1. Field of the Invention
The present invention relates to a document reading apparatus and method for reading a document which is fed onto a platen glass in an image processor such as an electrophotographic copying machine or an image scanner.
2. Description of the Prior Art
An automatic document feeding mechanism for automatically feeding a document to an image reader is used in an image processor such as an electrophotographic copying machine.
FIG. 1 shows one example of a conventional document reading apparatus. A document feeding mechanism 1 is mounted on an image processor unit 2, and is provided with a sheet feeding path 5, on which a document is fed onto a platen glass 4 from a sheet feeding tray 3 mounting the document thereon. The document fed from the sheet feeding tray 3 along the sheet feeding path 5 by supplying means, not shown, is fed by a feed roller 6 via the platen glass 4. The document is read by an image reader 7 in the image processor unit 2 while passing the platen glass 4, and then, is discharged to a sheet discharging tray 8 via a sheet discharging path 14 by the feed roller 6 and other feeding means, not shown.
A document end detecting sensor 9 is disposed upstream of the platen glass 4 on the sheet feeding path 5. The document end detecting sensor 9 is a photosensor of a reflection type, which sends a signal to a reading controller 20 in the image processor unit 2 upon detecting that the document fed by the feed roller 6 reaches a position of the document end detecting sensor 9.
The size of the document can be detected by a sensor, not shown, disposed in the sheet feeding tray 3 or on the sheet feeding path 5.
The reading controller 20 controls a reading timing of the image reader 7 in response to the signal sent from the document end detecting sensor 9. This control will be specifically explained below in reference to FIG. 2.
FIG. 2 illustrates the sheet feeding path 5 of FIG. 1 on a plane, wherein the sheet feeding path 5 is illustrated by an arrow indicative of its feeding direction.
The document end detecting sensor 9 is disposed upstream of the platen glass 4. A document 10 of a rectangle ABCD is fed along the sheet feeding path 5. As soon as a side “a” at the leading end of the document 10 reaches the document end detecting sensor 9, the sensor 9 outputs a detection signal. The reading controller 20 allows the image reader 7 to start reading after a lapse of a predetermined time after reception of the detection signal output from the sensor 9. Here, the predetermined time signifies a time taken to feed the document 10 by a distance “d” from a straight line L drawn on a detection point of the sensor 9 to the platen glass 4.
Since the size of the document 10 is previously detected, the reading controller 20 finishes the reading operation by the image reader 7 after a lapse of time corresponding to the length of the document 10 in the feeding direction. In other words, the image reader 7 is operative only for a period after the side “a” at the leading end of the document 10 reaches the platen glass 4 until a side “b” at a trailing end thereof reaches the platen glass 4.
In the case where the document 10 is obliquely fed in the above-described image reading apparatus, there may occur such inconveniences as described below.
As shown in FIG. 3, when the side “a” at the leading end of the document 10 fed obliquely to the sheet feeding path 5 crosses the straight line L drawn on the detection point of the document end detecting sensor 9, the sensor 9 detects the side “a” of the document 10. The reading controller 20 allows the image reader 7 to start the reading operation after a lapse of the predetermined time from that timing.
Thereafter, the reading controller 20 allows the image reader 7 to finish the reading operation at a timing at which a time corresponding to the length of the document which would be fed straight in the feeding direction elapses since the image reader 7 once starts the reading operation.
Namely, it is a region 11 indicated by a two-dot chain line in FIG. 3 that is actually read by the image reader 7. As a result, with respect to the obliquely fed document 10, only a portion overlapping with the region 11 is read. That is, a hatched portion 11a of the document 10 cannot be read, or is a deficiently read region.
In this manner, since there occurs the hatched, deficient region 11a, there arises a problem of a deficiently output image. In particular, in the case where a skew quantity, i.e., obliqueness is large, the deficiently read region 11a becomes large, and therefore, the deficiency of the output image becomes large accordingly.
In view of this, there has been another image processor in which a skew quantity of a document is detected, a read image is restored by rotating by the skew quantity, and then, is output. Nevertheless, however the output image may be rotated, a deficient portion at the time of a reading operation cannot be output. Namely, a partly deficient image is output straight at the best.